Tunable he omicron gamma delta mode dielectric resonator

ABSTRACT

A HE 0γδ  mode dielectric resonator ( 12 ) includes a cylindrical dielectric disk ( 32 ) having top and bottom ends ( 20, 22 ) spaced apart by a closed curve wall ( 24 ). The dielectric disk ( 32 ) has a dielectric constant greater than 40. An axially aligned hole ( 36 ) is formed through the disk ( 32 ) between the top and bottom ends ( 20, 22 ). A conductive wall ( 34 ) is formed at the closed curved wall ( 24 ) but not the top and bottom ends ( 20, 22 ). The hole ( 36 ) has a preferred diameter less than 0.2 times the diameter of the disk. A tuning plug ( 30 ) is formed from a material having a dielectric constant less than 0.5 times the dielectric constant of the dielectric disk ( 32 ) and an unloaded quality factor greater than 2.0 times the unloaded quality factor of the dielectric disk ( 32 ). The tuning plug is inserted to a desired depth within the hole ( 36 ) of the dielectric disk ( 32 ).

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to resonators used in RFcommunication and other equipment. More specifically, the presentinvention relates to a dielectric resonator configured to have a lowestresonant frequency in the HE_(0γδ) mode.

BACKGROUND OF THE INVENTION

[0002] Dielectric resonators are smaller than air cavity resonatorshaving equivalent resonant frequencies because wavelengths in thedielectric resonator are divided by the square root of the resonator'sdielectric constant. In addition, reactive power need not be storedstrictly inside the dielectric resonator, and fractional modes ofresonance are possible.

[0003] Unfortunately, for many applications conventional dielectricresonators are still undesirably large and/or made from exotic materialsthat are too costly. Mass market portable RF communication devicesrepresent one example of such applications. While most electronicsequipment benefits from smaller, less expensive components, portable RFcommunication devices receive particular benefit because of a heightenedneed to be as small and lightweight as possible, while being asinexpensive as possible to effectively compete in a highly competitivemarketplace.

[0004] U.S. Pat. No. 6,169,467, entitled “Dielectric ResonatorComprising A Dielectric Resonator Disk Having A Hole,” and having acommon inventive entity and assignee herewith is incorporated herein byreference. This patent teaches a TE_(0γδ) mode dielectric resonator,where “γ” indicates a fraction of periodicity in the radial direction,and “δ” indicates a fraction of periodicity in the axial direction. ThisTE_(0γδ) mode resonator achieves a relatively small size due, in part,to the fractional mode of resonance in two dimensions whilesimultaneously achieving an excellent quality factor (Q). Unfortunately,to achieve the excellent quality factor sacrifices were made thatresulted in a larger size and more expensive configuration than would bedesired for many applications. Moreover, while most all applicationsbenefit from a quality factor as high as possible, some applications donot require an excellent quality factor and can tolerate merely a goodquality factor.

[0005] A conventional practice in using dielectric resonators is toconfigure the resonator to resonate in a TE mode within a cavity and toincorporate an adjustable tuning device. Conventional tuning deviceshave an adjustable position relative to a dielectric resonator within aconductive cavity. The use of a conductive cavity having wallspositioned some distance away from the dielectric resonator is usefulfor maintaining as high a quality factor as possible, but increases sizeand cost accordingly. In some examples, the tuning devices areconductive members, but conductive tuning devices are not desiredbecause they are lossy and diminish the quality factor of the resonator.

[0006] In other examples, the tuning devices are dielectric membershaving as high a dielectric constant and quality factor as possible. Ahigh dielectric constant is desired to achieve an effective tuningrange. Often, a dielectric tuning member is made from the same materialas the dielectric resonator being tuned, but a material having an evengreater dielectric constant would be desirable to increase tuning range.The use of a common dielectric material for the resonator and the tuningmember is undesirable because dielectric materials tend to be expensive,and particularly expensive where small resonator size is a goal and moreexotic dielectric materials having higher dielectric constants are beingused. The use of a dielectric tuning member having a greater dielectricconstant than the dielectric constant of the dielectric resonator wouldbe even more expensive and therefore undesirable.

SUMMARY OF THE INVENTON

[0007] Accordingly, it is an advantage of the present invention that animproved HE_(γδ) mode dielectric resonator is provided.

[0008] Another advantage of the present invention is that a HE_(0γδ)mode dielectric resonator is provided which achieves a good Q in asmaller volume than required by a TE mode dielectric resonator or otherHE mode dielectric resonators at the same frequency.

[0009] Another advantage is that a tunable HE_(0γδ) mode dielectricresonator is provided.

[0010] Still another advantage is that a tunable HE_(0γδ) modedielectric resonator is provided wherein tuning is accomplished at verylow cost and with substantially no deterioration in quality factor.

[0011] The above and other advantages of the present invention arecarried out in one form by a tunable HE_(0γδ) mode dielectric resonator.This resonator includes a disk formed in the shape of a cylinder havinga diameter D. The disk is formed from a first dielectric materialconfigured to exhibit a dielectric constant ε_(r). The disk has firstand second opposing ends and a closed curve wall extending between thefirst and second ends. At least one of the first and second ends servesas a boundary between the disk and a second dielectric material. A holepenetrates the disk from the first end and extends toward the secondend. The hole exhibits a diameter less than 0.2D. The resonator alsoincludes a conductive coating on the disk wall and a dielectric tuningplug. The dielectric tuning plug has a dielectric constant less than0.5ε_(r) and extends into the hole in the disk. As a result, the tunableresonator has a lowest resonant frequency in a HE_(0γδ) mode ofoscillation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete understanding of the present invention may bederived by referring to the detailed description and claims whenconsidered in connection with the Figures, wherein like referencenumbers refer to similar items throughout the Figures, and:

[0013]FIG. 1 shows a cut-away perspective view of a physical layout fora circuit which includes a tunable HE_(0γδ) mode dielectric resonator;

[0014]FIG. 2 shows a cut-away side view of the tunable HE_(0γδ) modedielectric resonator; and

[0015]FIG. 3 shows a top view of the tunable HE_(0γδ) mode dielectricresonator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016]FIG. 1 shows a cut-away perspective view of a physical layout fora section of a circuit 10 which includes a tunable HE_(0γδ) modedielectric resonator 12. Circuit 10 is a microstrip circuit, such as maybe included in an oscillator or filter (not shown). Circuit 10 includesa conductive ground plane 14 underlying a dielectric substrate 16. Aconductive microstrip trace 18 is clad to the side of substrate 16 thatopposes ground plane 14.

[0017] Resonator 12 is preferably configured in a generally cylindricalgeometry and has a top end 20 which opposes a bottom end 22 and isspaced apart from bottom end 22 by a distance defined by a closed curvedwall 24 that extends between ends 20 and 22. Resonator 12 is mountednear trace 18 on the side of substrate 16 that carries trace 18. Bottomend 22 forms a boundary with substrate 16, and top end 20 forms aboundary with air 26. An axis of resonator 12 extends substantiallyperpendicular to substrate 16.

[0018] Resonator 12 may be mounted to substrate 16 using a suitabledielectric adhesive (not shown), or in any other manner known to thoseskilled in the art.

[0019] In the preferred embodiment, an electromagnetic signal having afrequency in the range of 0.3 to 10.0 GHz is impressed upon atransmission line formed from trace 18 and ground plane 14. While higherfrequency signals may also be used, the beneficial size advantages ofresonator 12 achieved for such higher frequencies are not as pronouncedas in the preferred frequency range of 0.3 to 10.0 GHz. This signalproduces a magnetic field having field lines surrounding trace 18, asdesignated by the letter H in FIG. 1. Due to the proximity of resonator12 to trace 18 and to the orientation of resonator 12, magnetic field His strongly coupled to resonator 12 in the tangential direction, whichextends between top and bottom ends 20 and 22 of resonator 12.

[0020] Of course, those skilled in the art will appreciate thatresonator 12 is not limited to being used in a microstrip circuit or tothe precise manner of coupling discussed above. Rather, microstripcircuit 10 merely represents one of many possible useful circuits withinwhich resonator 12 may be used.

[0021]FIG. 2 shows a side view and FIG. 3 shows a top view of a firstembodiment of HE_(0γδ) mode dielectric resonator 12. Referring to FIGS.1-3, resonator 12 is configured to have a lowest resonant frequency at afractional mode in both the radial and axial directions. The “γ” and “δ”subscripts in the HE_(0γδ) mode designation represent fractionalperiodicities in radial and axial directions, respectively. Inparticular, resonator 12 is formed from a tuning plug 30, a dielectricdisk 32, and a conductive wall 34.

[0022] Disk 32 is formed from a substantially homogeneous dielectricmaterial in the preferred embodiment. The selected material preferablyhas a dielectric constant (ε_(r))>40. In addition, this materialpreferably exhibits an unloaded quality factor (Q)>3000 in the desiredfrequency range of 0.3-10.0 GHz. Materials having higher dielectricconstants are more desirable than those with lower dielectric constantsbecause such materials allow the dimensions of resonator 12 to shrinkaccordingly for a given resonant frequency. Likewise, materials havinghigher Q values are more desirable than those with lower Q valuematerials because higher Q values allow resonator 12 to exhibit a higherquality factor.

[0023] Accordingly, the dielectric material from which disk 32 is formedis selected to balance a high dielectric constant parameter againstquality factor. Any of a variety of dielectric materials known to thoseskilled in the art which meet the desired dielectric constant andquality factor criteria may be used for disk 32.

[0024] Conductive wall 34, is desirably a highly conductive material,such as copper, silver or gold. In the preferred embodiment, conductivewall 34 is a coating that is applied to closed curve wall 24 ofresonator 12 so that it substantially entirely covers wall 24, butconductive wall 34 desirably does not cover a significant portion ofeither top or bottom ends 20 and 22.

[0025] As an applied coating, conductive wall 34 may be depicted inexaggerated thickness relative to the dimensions of disk 32 in thefigures for clarity. Not only does coating 34 refrain from coating topand bottom ends 20 and 22, but no other conductor is permitted tocontact top and bottom ends 20 and 22 in the preferred embodiment.

[0026] An axially aligned hole 36 penetrates into resonator 12 from thecenters of top and bottom sides 20 and 22 and extends entirely throughresonator 12 between sides 20 and 22. Resonator 12 has a cylinderdiameter D_(c). Cylinder diameter D_(c) defines the diameter ofdielectric disk 32, but conductive wall 34 may be sufficiently thin thatdiameter D_(c) can also be viewed as the diameter of resonator 12. Hole36 has a diameter D_(h) that allows resonator 12 to be effective whenless than 0.2D_(c). The use of a hole having this size, in combinationwith conductive wall 34, allows the HE_(0γδ) mode to be fundamental,with a TE_(0γδ) mode being the next highest resonant frequency. Allother things remaining constant, smaller holes are preferred to furtherseparate the HE_(0γδ) and TE_(0γδ) modes of resonance, but holes thatare too small lead to unreliable tuning and small tuning ranges.

[0027] Conductive wall 34 is not extended within hole 36. The boundaryof dielectric disk 32 within hole 36 and at top and bottom ends 20 and22 is formed with a different dielectric material. The dielectricconstants of these different boundary materials are desirablysignificantly less than dielectric constant ε_(r) of disk 32. Theseboundary materials include air 26 at top end 20 and inside a portion ofhole 36, tuning plug 30 inside a portion of hole 36, and substrate 16and/or an adhesive at bottom end 22. Effective results are achieved whensuch boundary materials exhibit dielectric constants less than 0.5ε_(r),where ε_(r) is the dielectric constant of disk 32.

[0028] Since dielectric resonator 12 is configured for HE moderesonance, tuning plug 30 is desirably formed from a dielectric materialhaving a significantly lower dielectric constant than the material fromwhich dielectric disk 32 is formed. A suitable tuning range andseparation between HE_(0γδ) and TE_(0γδ) modes of resonance can bemaintained when the dielectric constant of tuning plug 30 is less than0.5ε_(r), where ε_(r) is the dielectric constant of disk 32. In thepreferred embodiment, the dielectric constant of tuning plug 30 is lessthan 20 while the dielectric constant of disk 32 is greater than 40.

[0029] In order to maintain the quality factor of resonator 12 as highas possible, given the HE mode of resonance, tuning plug 30 exhibits anunloaded quality factor as high as practical. Desirably, the unloadedquality factor of tuning plug 30 in the frequency range of interest isgreater than 2Q, where Q is the unloaded quality factor of dielectricdisk 32. This parameter allows tuning to take place without exerting asignificant influence on the overall quality factor of resonator 12.

[0030] One material that is well suited for use as tuning plug 30 isalumina. Alumina typically exhibits a dielectric constant in the rangeof 4-10 and an unloaded quality factor greater than 10,000. In addition,alumina is mechanically stable, easily formed in desired shapes andsizes, readily available commercially, and relatively inexpensivecompared to materials conventionally used in forming useful dielectricresonators. Accordingly, alumina is an inexpensive material thatpromotes a wide tuning range for the HE_(0γδ) mode resonance, maintainsseparation between the HE_(0γδ) and TE_(0γδ) modes of resonancethroughout the tuning range, and does not significantly alter thequality factor of dielectric resonator 12 over the tuning range.However, those skilled in the art will appreciate that other materialsmay be used in forming tuning plug 30 with suitable results.

[0031] In the preferred embodiment depicted in the figures, tuning plug30 is dimensioned as a cylinder having indeterminate axial length and adiameter slightly smaller than the diameter D_(h) of hole 36 in disk 32.Tuning is accomplished by inserting tuning plug 30 into hole 36 throughtop end 20 of dielectric resonator 12 to a desired depth withindielectric resonator 12 where a desired resonant frequency is exhibited.Once this desired depth is reached, tuning plug 30 should extend withinhole 36 only partially through disk 32 between top and bottom ends 20and 22.

[0032] Desirably, the diameter of tuning plug 30 is sufficiently smallerthan diameter D_(h) so that different thermal expansion coefficientsexhibited by dielectric disk 32 and tuning plug 30 do not cause unduestress in tuning plug 30 or disk 32 as dielectric resonator 12 operatesover a desired temperature range. Otherwise, the diameter of tuning plug30 is desirably as large as possible within this constraint. When adesired depth is reached in the tuning process, a suitable dielectricadhesive fillet 38 may be applied between tuning plug 30 and dielectricdisk 32 to operate as a fastener that affixes tuning plug 30 todielectric disk 32 in a fixed relationship.

[0033] In another preferred embodiment (not shown) mating threads may beformed in tuning plug 30 and in the wall of dielectric disk 32surrounding hole 36 so that tuning plug 30 is inserted into andretracted from hole 36 by screwing or otherwise twisting. When a desireddepth is reached, adhesive fillet 38 may optionally be applied to locktuning plug 30 in place relative to disk 32. In this embodiment, suchmating threads may also serve as a fastener that affixes tuning plug 30to disk 32.

[0034] An axial length (L) defines the distance between top and bottomends 20 and 22. Resonator 12 is configured so that cylinder diameterD_(c) is roughly 0.5λ/{square root}{square root over (ε_(r))} or lessand so that axial length L of resonator 12 is less than 0.25λ/{squareroot}{square root over (ε_(r))}, where λ is the wavelength of the lowestresonant frequency of resonator 12 in empty space.

[0035] The electric field intensity within resonator 12 at the lowestresonant frequency experiences a zero at the electric wall formed atcurved wall 24 by the application of conductive wall 34. Accordingly,the dimensions of resonator 12, and particularly of cylinder diameterD_(c), exert a large influence on the lowest resonant frequency forresonator 12.

[0036] The forcing of the electric field intensity to equal zero at wall24 allows a standing wave to build within and without dielectricresonator 12 at a frequency having a wavelength determined by cylinderdiameter D_(c). Less than 0.5, and with preferential selection of holediameter D_(h) and dielectric constant ε_(r), less than 0.4, of awavelength resides within resonator 12 in the radial direction at thelowest resonant frequency. Likewise, by forming a boundary with a lowdielectric constant material at top and bottom ends 20 and 22, less then0.25 of a wavelength resides within resonator 12 in the axial directionat the lowest resonant frequency. In comparison with the TE_(0γδ) modedielectric resonator configured as described in U.S. Pat. No. 6,169,467,a savings in the volume of HE_(0γδ) mode dielectric resonator 12 of atleast 10%, and typically around 25%, is realized.

[0037] In summary, the present invention provides an improved HE_(0γδ)mode dielectric resonator. A HE_(0γδ) mode dielectric resonator isprovided which achieves a good Q in a smaller space than is required bya TE mode dielectric resonator or other HE mode dielectric resonators atthe same frequency. A tunable HE_(0γδ) mode dielectric resonator isprovided. The tunable HE_(0γδ) mode dielectric resonator is providedwherein tuning is accomplished at very low cost and with substantiallyno deterioration in quality factor.

[0038] Although the preferred embodiments of the invention have beenillustrated and described in detail, it will be readily apparent tothose skilled in the art that various modifications may be made thereinwithout departing from the spirit of the invention or from the scope ofthe appended claims. For example, while the present invention depictsround form factors for a dielectric disk and hole therein, those skilledin the art will understand that other form factors may be used togenerate equivalent dielectric resonators using the teaching providedherein.

What is claimed is:
 1. A tunable HE_(0γδ) mode dielectric resonatorcomprising: a disk formed in the shape of a cylinder having a diameter Dand formed from a first dielectric material configured to exhibit adielectric constant ε_(r), said disk having first and second opposingends and a closed curve wall extending between said first and secondends, said disk having a hole exhibiting a diameter less than 0.2Dpenetrating therein from said first end and extending toward said secondend, wherein at least one of said first and second ends serves as aboundary between said disk and a second dielectric material; aconductive coating on said wall; and a dielectric tuning plug having adielectric constant less than 0.5ε_(r) extending into said hole in saiddisk, wherein said resonator has a lowest resonant frequency in aHE_(0γδ) mode.
 2. A tunable HE_(0γδ) mode dielectric resonator asclaimed in claim 1 wherein said conductive coating covers substantiallysaid entire wall.
 3. A tunable HE_(0γδ) mode dielectric resonator asclaimed in claim 1 wherein said conductive coating does not cover asubstantial portion of said first end and said conductive coating doesnot cover a substantial portion of said second end.
 4. A tunableHE_(0γδ) mode dielectric resonator as claimed in claim 1 wherein saiddielectric material from which said disk is formed exhibits a dielectricconstant of at least
 40. 5. A tunable HE_(0γδ) mode dielectric resonatoras claimed in claim 1 wherein said hole extends through said disk fromsaid first end to said second end.
 6. A tunable HE_(0γδ) mode dielectricresonator as claimed in claim 1 wherein: said lowest resonant frequencyhas a wavelength λ; and said disk has a diameter less than λ/(2{squareroot}{square root over (ε_(r))}).
 7. A tunable HE_(0γδ) mode dielectricresonator as claimed in claim 1 wherein: said disk has an axial distanceof less than λ/(4{square root}{square root over (ε_(r))}).
 8. A tunableHE_(0γδ) mode dielectric resonator as claimed in claim 1 wherein saiddielectric tuning plug exhibits a dielectric constant of less than 20.9. A tunable HE_(0γδ) mode dielectric resonator as claimed in claim 1wherein said tuning plug is formed of alumina.
 10. A tunable HE_(0γδ)mode dielectric resonator as claimed in claim 1 wherein said tuning plugis affixed to said disk.
 11. A tunable HE_(0γδ) mode dielectricresonator as claimed in claim 10 additionally comprising a fastenercoupled to said tuning plug and said disk to retain said tuning plug ina fixed relationship to said disk.
 12. A tunable HE_(0γδ) modedielectric resonator as claimed in claim 1 wherein said tuning plugextends within said hole only partially through said disk between saidfirst and second ends.
 13. A tunable HE_(0γδ) mode dielectric resonatoras claimed in claim 1 wherein: said dielectric material from which saiddisk is formed exhibits an unloaded quality factor of Q; and saiddielectric tuning plug exhibits an unloaded quality factor greater than2Q.
 14. A tunable HE_(0γδ) mode dielectric resonator as claimed in claim1 wherein said second dielectric material is air.
 15. A tunable HE_(0γδ)mode dielectric resonator comprising: a disk formed in the shape of acylinder having a diameter D and formed from a first dielectric materialconfigured to exhibit a dielectric constant greater than 40, said diskhaving first and second opposing ends and a closed curve wall extendingbetween said first and second ends, said disk having a hole exhibiting adiameter less than 0.2D penetrating therein from said first end andextending toward said second end, wherein at least one of said first andsecond ends serves as a boundary between said disk and a seconddielectric material; a conductive coating on said wall; and a dielectrictuning plug extending into and affixed to said disk, said dielectrictuning plug exhibiting a dielectric constant of less than 20, whereinsaid resonator has a lowest resonant frequency in a HE_(0γδ) mode.
 16. Atunable HE_(0γδ) mode dielectric resonator as claimed in claim 15wherein said tuning plug is formed of alumina.
 17. A tunable HE_(0γδ)mode dielectric resonator as claimed in claim 15 wherein: saiddielectric material from which said disk is formed exhibits an unloadedquality factor of Q; and said dielectric tuning plug exhibits anunloaded quality factor greater than 2Q.
 18. A tunable HE_(0γδ) modedielectric resonator as claimed in claim 15 wherein: said lowestresonant frequency has a wavelength λ; and said disk has a diameter lessthan λ/(2{square root}{square root over (ε_(r))}).
 19. A tunableHE_(0γδ) mode dielectric resonator as claimed in claim 18 wherein: saiddisk has an axial distance of less than λ/(4{square root}{square rootover (ε_(r))}).
 20. A tunable HE_(0γδ) mode dielectric resonatorcomprising: a disk formed from a first dielectric material exhibiting adielectric constant ε_(r) greater than 40 and an unloaded quality factorof Q and formed in the shape of a cylinder having a diameter D less thanλ/(2{square root}{square root over (ε_(r))}), wherein λ is a wavelengthof a lowest resonant frequency of said resonator, said disk having firstand second opposing ends and a closed curve wall extending between saidfirst and second ends, said disk having an axial distance between saidfirst and second ends of less than λ/( 4{square root}{square root over(ε_(r))}), and said disk having a hole exhibiting a diameter less than0.2D extending from said first end to said second end, wherein at leastone of said first and second ends serves as a boundary between said diskand air; a conductive coating on said wall; and a dielectric tuning plugextending into and affixed to said disk, said dielectric tuning plugexhibiting a dielectric constant of less than 20 and a quality factorgreater than 2Q, wherein said resonator has a lowest resonant frequencyin a HE_(0γδ) mode.